Laminates with adhesives containing aliphatic nitro compounds

ABSTRACT

Adhesive compositions containing aliphatic nitro compounds.

United States Patent [191 Hausch et al.

[ Oct. 28, 1975 LAMINATES WITH ADI-IESIVES CONTAINING ALIPI-IATIC NITROCOMPOUNDS [75] Inventors: Walter R. Hausch; John W.

Fieldhouse; Edward L. Kay, all of Akron, Ohio 73 Assignee: The FirestoneTire & Rubber Company, Akron, Ohio [22] Filed: Oct. 15, 1974 [21] Appl.No.: 514,343

Related US. Application Data [62] Division of Ser. No. 383,733, July 30,1973, Pat. No.

[52] US. Cl. 428/423; 156/110 A; 156/331;

[56] References Cited UNITED STATES PATENTS 3,503,845 3/1970 l-lollatzet al. 161/190 Primary Examiner-George F. Lesmes Assistant Examiner-R.J. Roche [5 7] ABSTRACT Adhesive compositions containing aliphatic nitrocompounds.

5 Claims, No Drawings LAMINATES WITH ADHESIVES CONTAINING ALIPI-IATICNITRO COMPOUNDS This is a division of application Ser. No. 383,733,filed July 30, 1973, now US. Pat. No. 3,880,808.

FIELD OF THE INVENTION This invention relates to obtaining improvedadhesion between polyurethane rubbers and olefinic rubbers or othersubstrates including metals. By polyurethane rubbers are meant therubbers produced by reaction of relatively high molecular weightpolyester or polyether resins with polyisocyanates. By olefinic rubbersare meant those rubbers containing olefinic unsaturation in theirpolymer chains such as natural rubber, synthetic polyisoprene (IR),polybutadiene (BR), rubbery copolymers of butadiene and styrene (SBR),rubbery copolymers of butadiene and acrylonitrile (NBR), rubberycopolymers of isoprene and isobutylene (IIR),

polychloroprene (CR), ethylene-propylene rubbers (EPDM) and the like.This invention has particular use in applications where strength of ahigh degree is important as in production of tires, belting, industrialrubber articles and like products composed of both polyurethane rubberand olefinic rubber components.

PRIOR ART It is known from US. Pat. No. 2,905,582 that bonding of apolyurethane rubber to an olefinic rubber can be realized by interposingbetween such rubbers an adhesive including in combination an organicisocyanate and an aromatic compound containing at least one nitrosogroup attached directly to a ring carbon atom. The aromatic nitrosocompounds contemplated by this patent are those wherein one or more ofthe molecular hydrogens of the aromatic nucleus is replaced by alkyl,alkoxy, cycloalkyl, aryl, arylalkyl, arylamine, arylnitrosoamine,halogen and like groups. This patent suggests that its adhesivecompositions contain in addition to the described aromatic nitrosocompounds and isocyanates also a so-called organic film-forming materialsuch as a natural or synthetic elastomer or resin and it is furthercontemplated by the patent that tires be produced by adhering apolyurethane rubber tread to an olefinic rubber body.

SUMMARY OF THE INVENTION While this invention also relates to adhesivecompositions comprising an organic isocyanate and often for best resultsan organic film-forming material, the adhesives compositions of thisinvention contain also an aliphatic nitro compound as an adhesionpromoter. To applicants knowledge aliphatic nitro compounds have notheretofore been employed as adhesion promoters. Aliphatic nitrocompounds employed in this invention are illustrated by the followinggeneralized formula:

wherein R R and R are selected from the group consisting of hydrogenatoms, hydrocarbyl groups and halogen atoms. R,, R and R may be the sameor differ- 2 ent; that is any combination of hydrogen atom, hydrocarbylgroup, and halogen atoms are suitable.

The hydrocarbyl group may contain from one to about 16 carbon atomsarranged in a straight or branched chain configuration. The chain may besaturated or unsaturated. The hydrocarbyl group may be a cyclic or anaromatic structure or any combination of these structures. Thehydrocarbyl groups may also contain halogen atoms, preferably chlorineor bromine atoms. The hydrocarbyl groupds may also contain functionalgroups such as hydroxyl, mercapto, ether,

thioether, carbonyl, thiocarbonyl, carboxyl ester,

amino, imino and amide groups or combinations of same.

As indicated one or more of R R and R may be halogen atoms, chlorine andbromine atoms being preferred. Based on commercial availability,chlorine compounds are preferred over bromine compounds.

Vicinal dinitroalkanes or, for that matter, alkanes with any pluralityof nitro functions also function as adhesion promoters in our inventionsso long as the number of nitro functionalitiesis not sifficient to causethe compound to be unstable.

Illustrative of compounds useful in the practice of our invention isnitromethane wherein all R groups of the generalized formula arehydrogen atoms. Monoalkyl derivatives or nitromethane such asnitroethane, l-nitropropane, l-nitrobutane and the like illustratecompounds wherein one R group is a straight chain aliphatic group,Additionally, the following compounds, being named as derivatives ofmethane are useful in our invention: dimethylnitromethane(2-nitropropane in a following example), trimethylnitromethane,diethylni tromethane, triethylnitromethane, di-n-propylnitromethane,tri-n-propylnitromethane and the like.

Examples of aliphatic nitrocompounds containing branched hydrocarbylgroups useful in the invention are l-nitro-3-methylbutane, and2,6-dimethyl-4- nitroheptane and the like. Examples wherein thehydrocarbyl group is of a cyclic configuration arecyclohexylnitromethane, bis(cyclohexyl)nitromethane,tris(cyclohexyl)nitromethane, cycloheptylnitromethane and the like.

Illustrations of useful aliphatic nitro compounds wherein thehydrocarbyl group is unsaturated are 3- nitropropenel ,4-nitrobutenel4-nitrobutene-2, 3- nitropentadienel ,4, 3-nitroheptadiene-2,5 3-nitroheptadiene-1,6 and the like. Illustrative of aliphatic compounds ofthe invention in which the hydrocarbyl group is aromatic arephenylnitromethane, bis(- phenyl)nitromethane, tris(phenyl)nitromethane,orthomethylphenyl-nitromethane, bis(orthomethylphenyl)nitromethane,tris(orthomethylphenyl)nitromethane and the like.

Examples of aliphatic halogenated aliphatic nitrocompounds of theinvention are chloronitromethane, dichloronitromethane,bromonitromethane, dibromonitromethane, l-chlorol -nitroethane,2-chlorol -nitroethane, l -chlorol -nitropropane, 2-chlorolnitropropane, 3-chlorol -nitropropane, nitropropane,2-chloro-2nitropropane and the like.

Illustrative compounds of the invention wherein R R and R arecombinations of structures previously referred to areethyl-iso-propylnitromethane, ethyl-isopropyl-cyclohexyl-nitromethane,ethyl-cyclohexylphenylnitromethane,isopropylcyclohexyl-phenylnitromethane,ethyl-isopropyl-chloronitromethane, ethl -chloro-2-- yl-iso-propyl-(2-chlorocyclohexyl)nitromethane, ethyliso-propyl-(2-chlorophenyl)nitromethane and the like.

Illustrative compounds of the invention with a plurality ofnitrofunctions are 1,2-dinitroethane, 1,3-dinitropropane, 1,2-dichloro-1 ,2-dinitroethane, 1 ,3-dichlorol ,3-dinitropropane,2,2-dichlorol ,3-dinitropropane, 1,2,3-trinitropropane, l,2,3-trichloro-l ,2,3-trinitropropane and the like.

ADHESION TESTS The adhesion test results reported hereafter wereobtained on laminates of olefinic rubber and polyurethane rubber, acement in accordance with the invention having been interposed betweenthe two rubbers. The procedure follows.

First, a sheet 6 inches square and 0.100 inch thick was prepared from avulcanizable olefinic rubber compound. One side of the olefinic rubbersheet was backed with reinforcing nylon tire fabric treated foradhesion. This sheet was cured (usually of the order of 20 to 30 minutesat about 300F.). The cured olefinic rubber sheet was buffed to a satinyfinish on the side opposite the tire fabric, the buffed surface beingwashed with acetone or white gasoline. A 2 by 6 inch portion of thebuffed surface in a direction perpendicular to the direction of the tirecord of the fabric was covered with holland cloth, the holland clothbeing securely taped down on all four edges. The exposed buffed surfaceof the cured olefinic rubber sheet was then coated with the adhesivecement of the invention being tested and allowed to dry. The olefinicrubber sheet was then placed in the bottom of a 6 by 6 by 0.250 inchmold with the adhesive cement coated surface up. A curable liquidpolyurethane rubber compound was poured into the mold in a sufficientquantity to fill the mold. After the polyurethane material had gelled a6 by 6 inch piece of square woven nylon was placed on the surface of thepolyurethane. A cover plate was placed on the top of the mold and themold was heated 3 hours at 212F. to complete the curing of thepolyurethane rubber. Flashing was trimmed from the resulting testlaminate and the edge containing the holland cloth was cut back toexpose the cloth. One inch wide test strips were cut from the laminatein a direction parallel to the direction of the reinforcing tire cord.After 24 hours room temperature test results were obtained by clampingthe free ends of a given test strip to the jaws of a testing machine andthe jaws of the test machine were pulled apart at a rate of 2 inches perminute, the force in pounds per inch at tear as well as the nature ofthe tear being observed. With regard to the nature of the adhesion, theterms Pad Tear, Rubber Tear, Urethane Tear and Adhesive Failure as theymay appear hereafter have the following meanings. Pad Tear means thatthe tear was along the fabric. Rubber Tear means that the tear was inthe olefinic rubber. Urethane Tear means that the tear was in thepolyurethane rubber. Adhesive Failure means that the tear was along theinterface between the polyurethane rubber and the olefinic rubber. Wherethe percentage of tear reported hereafter is less than 100%, the balancewas tear along the interface. For elevated temperature testing the testsamples were placed in an oven maintained at the desired elevatedtemperature at 5 minute intervals. Each test sample was then removedafter being in the oven a total of minutes and immediately subjected tothe pulling test.

4 The following examples illustrate practice of the invention. In theexamples the vulcanizable olefinic rubber sheets employed were preparedof the following formulation:

Parts by Weight SBR 60.0 Polybutadiene 40.0 Carbon black 70.0 Oil 44.0Zinc Oxide 2.0 Stearic acid 2.0 Wax 3.0 Sulfur 1.7 Accelerator 1.2Antioxidant 10 Parts by Weight Adiprene L-167* 100.00 Silicone DC-200**0.10 Methylene bis(o-chloro- 20.98 p-aniline) Dioctyl phthalate Apolyurethane rubber supplied by E. l. duPont de Nemours & Co., lnc. Asilicone oil supplied by Dow Corning Corporation.

EXAMPLE I A cement containing an adhesion promoter of the invention wasprepared of the following formulation:

Grams Nitroethane 0.75 Adiprene L-l67 1.50 Toluene diisocyanatc 3 .00

Following the above outlined procedure, adhesion test strips wereproduced employing this cement to adhere the described olefinic rubberto the described polyurethane rubber. The test results obtained were asfollows:

Adhesion, Test Temperature lbs/in. Nature of Adhesion Room 120 l007crubber tear 212F. 60 rubber and pad tear 250F. 60 l00% rubber tearEXAMPLE ll A cement containing an adhesion promoter of the invention wasprepared of the following formulation:

Grams Z-Nitroprop ane 0.75 Adiprene L-l67 [.50 Toluene diisocyanate 3.00

Following theabove outlined procedure, adhesion test strips wereproduced employing this cement to adhere the described olefinic rubberto the described polyure-, thane rubber. The test results obtained wereas follows;

A cement containing an adhesion promoter of the in- 'vention wasprepared of the following formulation:

Grams l-chlorol-nitropropane 0.75 Adiprene L-l67 1.50 Toluenediisocyanate 3.00 Toluene 3.00

Following the above outlined procedure, adhesion test strips wereproduced employing this cement to adhere the described olefinic rubberto the described polyurethane rubber. The test results obtained were asfollows: 3

Adhesion Test Temperature lbs.lin. Nature of Adhesion Room 120 100%urethane tear 212F. 50 75% rubber tear and 25% pad tear 250F. 83 100%urethane tear EXAMPLE IV A cement containing an adhesion promoter of theinvention was prepared of the following formulation:

Grams 2-ch1oro-2-nitropropane 0.75 Adiprene L- l 67 3.00 Toluenediisocyanate 1.50 Toluene 3.00

Grams l ,B-dinitroneopentane 0.75 Adiprene L-l 67 1.50 Toluenediisocyanate 3.00 Toluene 3.00

Following the above outlined procedure, adhesion test strips wereproduced employing this cement to adhere the described olefinic rubberto the described polyurethane rubber. The test results obtained were asfollows:

Adhesion, Test Temperature 1bs./in. Nature of Adhesion Room .70 50%rubber tear 212F. 5% rubber tear 250F. 17 5% rubber tear As shown by theresults reported in the above examples, excellent adhesion is obtainedby the use of ce- 0 polymers are suitable film formers. Other suitablefilm formers useful in the'practice of the invention are the natural andsynthetic elastomers generally including without limitation the olefinicrubbers aforementioned as well as telechelic polymers and olefinicresins and 5 their halogen containing analogs, condensation polymerssuch as phenol-aldehyde and epoxy resins, polyamides, polyesters, andthe like. Further suitable film formers include halogenated waxes.

Although toluene diisocyanate was used to illustrate our invention,other suitable isocyanates include phenylisocyanate, tolylisocyanate,xylene diisocyanate, cumene diisocyanate,methylenebis(p,p'-phenylisocyanate), methylenebis(p,p-tolylisocyanate),methylenebis(p,p'-xylylisocyanate) and the like. Triisocy- 5 anates orhigher will also function but are generally Following the above outlinedprocedure, adhesion test strips were produced employing this cement toadhere the described olefinic rubber to the described polyurethanerubber. The test results obtained were as follows:

A cement containing an adhesion promoter of the invention was preparedof the following formulation:

more expensive and less readily available on a commercial scale. Toluenediisocyanate is preferred on the basis of commercial availability.So-called blocked isocyanates which release the isocyanate at specifiedtemperatures will also function provided that the release temperature islower than the cure temperature of the composite. Representative blockedisocyanates are phenol blocked, caprolactam blocked isocyanates. Dimericisocyanates are also applicable. Organic isothiocyanates such asphenylisothiocyanate are also applicable. Another criterion forselection of an isocyanate is whether it would have a tendency todiscolor the substrate. For example, Hylene W* is essentiallynon-staining and would be preferred on this basis.

*Methylenebis(4,4'-cyclohexylisocyanate) supplied by E. 1. duPont deNemours and Co., lnc.

Although toluene is used above as a solvent as a matter of convenience,benzene, xylenes, tetrahydrofuran, dimethylylforrnamide or many othercommon organic solvents as well as toluene are suitable. Any aprotoicsolvent should be efiective. 1n the case the adhesion promoter isliquid, the solvent may be deleted.

The exact concentrations of the film former, adhesion promoter andisocyanate will depend on the ranges:

Parts by Weight Film Former l 9O Adhesion Promoter 1.00 60 1.00 95lsocyanate The data supplied in the Examples demonstrates the utility ofthe adhesion promoters of the invention for adhering of rubber topolyurethane. The data are indicative that the adhesive formulationsgive good results with rubber to rubber and urethane to urethane. Aparticularly desirable application of the adhesives of the inventioninvolves the adhesion of olefinic rubber tire treads to polyurethanerubber tire bodies and conversely in adhering polyurethane rubber tiretreads to olefinic rubber tire bodies. Since good adhesion results areobtained using a polyurethane film former based on either a polyether ora polyester, good adhesion of either an olefinic rubber or apolyurethane rubber to polyesters also is obtained by the adhesives ofthe invention.

A further application of the invention involves treatment of rubberarticles with the adhesive formulations of the invention as a means ofpriming the surface for painting with a urethane based paint or with anacrylate based paint.

Generally, we believe that the adhesive formulations as herein disclosedwould be effective for adhering olefinic rubber to thermoplastic orthermosetting resins such as polystyrene, polyalphamethylstyrene,polyvinylchloride, polyvinylidenechloride, polyacrylates,polymethacrylates, polyacrylonitrile, polyesters, polyamides, etc. Theadhesive formulations should also be effective for adhering thesethermoplastic or thermosetting resins to themselves or to any member ofthe above-mentioned groups. The adhesive formulations as hereindisclosed would also be effective for adhering olefinic rubbers orpolyurethane rubbers to themselves or to metals, glass, ceramics, softand hard woods as well as adhering together any combination of thepreceding substrates.

What is claimed is:

1. An adhesively-bonded laminate, layers of said laminate being bondedtogether by an adhesive composition comprising an organic isocyanate, anorganic filmforming material and as an adhesion promoter an aliphaticnitro compound of the formula:

wherein R R and R are selected from the group consisting of hydrogenatoms, hydrocarbyl groups and halogen atoms.

2. An adhesively-bonded laminate in accordance with claim 1 whereinolefinic rubber is bonded to polyurethane rubber.

3. An adhesively-bonded laminate in accordance with claim 1 whereinolefinic rubber is bonded to olefinic rubber.

4. An adhesively-bonded laminate in accordance with claim 1 whereinpolyurethane rubber is bonded to polyurethane rubber.

5. An adhesively-bonded laminate in accordance with claim 1 whereinolefinic rubber is bonded to polyester.

1. AN ADHESIVELY-BONDED LAMINATE, LAYERS OF SAID LAMINATE BEING BONDEDTOGETHER BY AN ADHESIVE COMPOSITION COMPRISING AN ORGANIC ISOCYANATE, ANORGANIC FILM-FORMING MAERIAL AND AS AN ADHESION PROMOTER AN ALIPHATICNITRO COMPOUND OF THE FORMULA:
 2. An adhesively-bonded laminate inaccordance with claim 1 wherein olefinic rubber is bonded topolyurethane rubber.
 3. An adhesively-bonded laminate in accordance withclaim 1 wherein olefinic rubber is bonded to olefinic rubber.
 4. Anadhesively-bonded laminate in accordance with claim 1 whereinpolyurethane rubber is bonded to polyurethane rubber.
 5. Anadhesively-bonded laminate in accordance with claim 1 wherein olefinicrubber is bonded to polyester.